Transient analysis of forced circulation solar water heating system

This paper presents a transient analysis of a solar water heating system with forced circulation. Two modes of hot water retrieval have been taken into account viz direct from the tank and through a heat exchanger placed in the tank. Analysis has been presented both for constant flow and constant collection temperature modes. Effects of heat exchanger length and time of starting hot water retrieval on the system performance have also been studied. Numerical calculations have been made for a typical cold day (26 January, 1980) at Delhi.     

Transient analysis of forced circulation solar water heating system with collectors in series

This communication presents an analysis of the thermal performance of a hot water system consisting of N collectors in series with a storage tank; forced circulation and withdrawal of hot water by displacement with cold water are built into the thermal model. Two modes of withdrawal of hot water, viz. (i) constant flow rate and, (ii) constant hot water temperature (during the day), have been considered. For a quantitative appreciation of the results, numerical calculations have been made for the two modes of hot water withdrawal corresponding to a typical cold day (26 January, 1980) in Delhi.     

Optimal design of a forced circulation solar water heating system for a residential unit in cold climate using TRNSYS

An indirect forced circulation solar water heating systems using a flat-plate collector is modeled for domestic hot water requirements of a single-family residential unit in Montreal, Canada. All necessary design parameters are studied and the optimum values are determined using TRNSYS simulation program. The solar fraction of the entire system is used as the optimization parameter. Design parameters of both the system and the collector were optimized that include collector area, fluid type, collector mass flow rate, storage tank volume and height, heat exchanger effectiveness, size and length of connecting pipes, absorber plate material and thickness, number and size of the riser tubes, tube spacing, and the collector’s aspect ratio. The results show that by utilizing solar energy, the designed system could provide 83-97% and 30-62% of the hot water demands in summer and winter, respectively. It is also determined that even a locally made non-selective-coated collector can supply about 54% of the annual water heating energy requirement by solar energy.     

Improved differential control for solar heating systems

One possibility to exploit solar energy better is the efficiency enhancement of the control of solar thermal heating systems. In this paper an improved differential control and the generally used ordinary differential control operating with fixed switch-on and switch-off temperature differences are compared in different efficiency viewpoints. The comparison is based on measured data of a particular system at the Szent István University, Gödöll? and on a TRNSYS model developed for solar heating systems. According to the results the improved control provides a higher value of utilizability and brings forth fewer switch-ons and switch-offs for the pumps. These advantages nevertheless result in extended operation time and thus extended parasitic consumption of the pumps. This drawback can, however, be moderated or even extinguished by modern pumps with low energy consumption or if supplied by renewable energy source. Comparing the amount of utilized solar energy and consumed parasitic energy increments, the improved control can be generally recommended.     

Transient analysis of closed loop solar water heating system

This paper presents a simplified transient analysis of a forced-circulation solar water heating system with a heat exchanger in the collector loop. Besides two modes of hot water withdrawal viz constant flow and constant collection temperature; the paper also studies the effectiveness of the flow through the heat exchanger and its length. The system performance has been further studied by considering different timings of starting hot water withdrawal. Calculations have been made for a typical cold day (26 January 1980) in New Delhi.     

Incentives for solar water heating systems

Life-cycle costing has been used in an economic analysis of three solar domestic hot water installations. These are in operation in Las Palmas (Canary Islands) and are backed by conventional installations consuming either fuel-oil (GG), butane (BB) or electricity (EE). The cumulative cost flows (CCF), including expenditures for purchase, recovery, maintenance, fuel and operating costs, are calculated over the useful life of the installations for expected annual fuel-increment rates. Twenty-seven comparisons are made between the solar (SAS) and conventional systems (CS). Total savings are found over the lifetime and the repayment periods are obtained as a function of discount rate. The SAS and CS are examined with respect to economic incentives such as subvention, tax deduction, loans and their combinations. Finally, the variations of the payback periods and rates of return on investment (IRR) are plotted against the fuel price, annual fuel increment rate and initial investment in the SAS for a wide range of economic parameters.     

Optimal temperature control of solar heating systems

Temperature control systems based on solar and wind energy differ in two important ways from existing fossil fuel systems. One is that solar systems, at least active solar systems, all have some kind of energy storage, the other is that the source of energy in a solar and wind energy system is variable and uncontrollable. Because of these added complications and the high capital investment required for solar and wind energy systems, considerably more sophisticated techniques are required for the design of those systems. In this study, a new technique is applied to the optimal control problem of solar heating systems.     

Augmented control strategies for radiant floor heating systems

A dynamic model of a radiant floor heating (RFH) system useful for control analysis is developed. The overall model consists of a boiler, distribution system, an embedded tube floor slab and building enclosure. The overall model is described by non‐linear differential equations which were solved using finite numerical methods. Two control strategies for improving the temperature regulation in RFH systems are proposed. These are: a multistage on–off control and an augmented constant gain control (ACGC). Simulation results show that the multistage control maintains zone air temperature close to the setpoint better than the existing on–off control scheme does. Likewise, ACGC gives good zone temperature control compared to the classical proportional control. The ACGC is shown to be robust to changes in weather conditions and internal heat gains. The advantage of the control strategies proposed is that they eliminate the use of outdoor temperature sensors required in some existing control schemes. Being simple and robust, the proposed control schemes are good candidate controls for RFH systems. Copyright © 2002 John Wiley & Sons, Ltd.     

Optimal flow control of a forced circulation solar water heating system with energy storage units and connecting pipes

This paper focuses on pump flow rate optimization for forced circulation solar water heating systems with pipes. The system consists of: an array of flat plate solar collectors, two storage tanks for the circulation fluid and water, a heat exchanger, two pumps, and connecting pipes. The storage tanks operate in the fully mixed regime to avoid thermal stratification. The pipes are considered as separated components in the system so as to account for their thermal effects. The objective is to determine optimal flow rates in the primary and secondary loops in order to maximize energy transfer to the circulation fluid storage tank, while reaching user defined temperatures in the water storage tank to increase thermal comfort. A model is developed using mainly the first and second laws of thermodynamics. The model is used to maximize the difference between the energy extracted from the solar collector and the combined sum of the energy extracted by the heat exchanger and corresponding energies used by the pumps in the primary and secondary loops. The objective function maximizes the overall system energy gain whilst minimizing the sum of the energy extracted by the heat exchanger and corresponding pump energy in the secondary loop to conserve stored energy and meet the user requirement of water tank temperatures. A case study is shown to illustrate the effects of the model. When compared to other flow control techniques, in particular the most suitable energy efficient control strategy, the results of this study show a 7.82% increase in the amount of energy extracted. The results also show system thermal losses ranging between 5.54% and 7.34% for the different control strategies due to connecting pipe losses.     

An experimental investigation into the performance of a domestic forced circulation solar water heater under varying operating conditions

An experimental investigation is carried out on a forced circulation solar water heater to assess its performance under various operating conditions. The system consisted of two identical collectors of total absorber area of 3.45 m² and a storage tank of 200 litre capacity. Experiments were carried out during clear days with and without system loading for two water mass flow rates through the collector; namely 0.1305 kg/s and 0.06525 kg/s. The system was operated without thermostat control and with thermostat control at maximum and minimum settings. The collector efficiency improved with system loading. The improvement was better with increased hot water withdrawal from the system.     

An improved design method for solar water heating systems

In this paper, the $\text{Φ}$,f-chart method is extended to open-loop solar hot water heating systems. This method is an improvement over the f-chart method since it does not impose any restrictions on the water set temperature, water mains temperature, or the preheat tank loss coefficient. The procedure is general for both one-tank and two-tank systems. The modified $\text{Φ}$,f-chart method is still applicable to the closed-loop systems for which it was originally developed.     

太阳能热水系统技术方案

图1凡是使用过接触过或关注过太阳热水器(或系统)的人都会得出这样的认识:尽管太阳热水器有着其它热水器(油、电、气)无可比拟的节能、环保、安全等优点,但它也确实存在着其它热水器所不存在的令人头疼的难题,诸如:防冻、抗冻问题;一年四季24小时供应热水问题;与建筑物有机结合问题以及恒温,恒压出水问题。这些问题中任何一个问题的根本解决,都会对太阳能热利用起到很大的推动作用。如果能全部加以解决,那将对目前3种热水器的市场格局产生决定性的影响。能不能找到一种技术方案,把这所有的难题一下子全部加以解决呢?通过多年摸索与工程实践,…     

也谈全天候太阳能热水系统

何谓“全天候太阳能热水系统”，简单的说就是一年365天、每天24小时，时时都有热水备用的太阳能热水系统及工程。让用户(包括集体用户和家庭用户)再也不用为“现在洗浴有热水吗”而操心。它比过去使用过的“天天有热水”，实际上是天天的某个时段才有热水的承诺有更加明确的概念界限。也让用户遇到阴雨风雪等恶劣天气环境时无后顾之忧。     

Transient analysis of parallel plate forced circulation solar water heating system

In this paper, a transient analysis of a forced circulation solar water heating system with and without heat exchangers in the collector loop and storage tank has been presented for a parallel flat plate collector. The effect of various water heating system parameters on its performance have been studied. Numerical calculations have been made for a typical cold day viz. 26 January 1980 in Delhi.     

家用太阳热水器与太阳热水系统的技术经济比较

分析了户用太阳热水器和太阳热水系统工程的经济技术特点,对两者成本构成、项目财务净现值、投入回收期和财务内部收益率等有关指标进行了经济技术比较.分析比较表明,太阳热水系统与家用热水器相比,节省安装占地,与建筑相结合得好,在降低成本,缩短投资回收期,提高经济效益方面有明显的优势.     

Analysis of natural circulation solar water heating systems

This paper presents an analysis of the performance of a solar water heating system with natural thermosyphon circulation between the collector and the storage tank. The analysis is based on the formulation by Ong except that provision for withdrawal of hot water from the tank (for domestic/ industrial use) has been made in the energy balance equation; further in contrast to the use of the finite difference method by Ong, explicit expressions have been obtained. The results of the present analysis (in the absence of withdrawal of hot water from the tank) are seen to be in better agreement with experiments than the corresponding results of Ong, obtained by use of the finite difference method.

Numerical results, corresponding to hot water retrieved from the storage tank, have been presented for two modes of hot water withdrawal viz. the constant flow rate and constant mean storage tank water temperature.     

Experimental investigation of temperature and flow distribution in a thermosyphon solar water heating system

Natural circulation solar water heating systems are available in varying collector geometries (and materials), storage tank capacities and specifications of individual components. Though theoretical and experimental studies including the test procedures are available to estimate the performances of these systems, detailed experimental studies showing the temperature profiles of the absorber plate, water temperature in the riser and water flow in the riser are few. This paper presents details of experimental observations of temperature and flow distribution in a natural circulation solar water heating system and its comparison with the theoretical models. The measured profile of the absorber temperature near the riser tubes (near the bottom and top headers) conforms well with the theoretical models. The values at the riser tubes near the collector inlet are found to be generally much higher than those at the other risers on a clear day, while on cloudy days, these temperatures are uniform. The mean absorber plate and mean fluid temperature during a day has been estimated and compared with theoretical models. The temperature of water near the riser outlets was found to be fairly uniform especially in cloudy and partly cloudy days at a given plane during a day. The temperature of water in the riser depends on its flow rate. Measurements of glass temperature were also carried out.     

Performance of n forced circulation water heating systems in series

This paper presents an analytical investigation of the thermal performance of a forced circulation solar water heating system in which n water heating systems are connected in series. Numerical calculations have been made for a typical cold day (26 January 1980) in Delhi, India, and some interesting conclusions have been presented.